the answer that involves the least amount of conspiracies is that a guy accustomed to partying as hard as physically possible as a coping mechanism 100% of the time looked at his future (life in prison, no coping mechanisms available) and just took the only exit, and he was able to do this because fancy expensive prison for rich people halfassed procedure to make the fancy rich prisoners comfy

an answer that involves slightly more conspiracies is above, but someone else made some phone calls to arrange for the conditions that allowed him to do it unnoticed, to stop him from testifying (0 evidence of this)

“oh but actually John Hitman tunneled in through the airvents and strangled him” no, stupid, stop, bad